In view of problems of the Wireless Personal Area Network (WPAN) MAC protocol of the IEEE standard 802.15.3, which is based on a centralized-control protocol, the Multi-Band OFDM (Orthogonal Frequency Division Multiplexing) Alliance (MBOA) group started its MBOA MAC subgroup. To address the problems of the IEEE 802.15.3 MAC such as Simultaneous Operating Piconet and Mobility issues, the MBOA MAC is based on a distributed protocol rather than a centralized-controlled one. In order for every device to be able to form a network by itself, each device is required to beacon in a distributed fashion. The MBOA MAC v0.5 defines the superframe of a device to be of 65536 μs. The superframe is to be composed of 256 Media Access Slots (MASs) where each MAS length is 256 μs. The first 8 MASs of a superframe, relative to an individual group, are defined as a Beacon Period (BP) and are sub-divided into 24 Beacon Slots (BSs). The rest of the MASs in the superframe are used for data transfer, employing either EDCA (Enhanced Distributed Channel Access) (data contention method) or DRP (Distributed Reservation Protocol) (data reservation method). The superframe 100 of MBOA MAC is illustrated in FIG. 1.
Devices powering up first scan the medium for any existing network by listening to beacon frames. If beacon frames are heard, each device attempts to broadcast their beacon in a randomly selected vacant BS. Devices receive the BS occupancy information via the beacon of neighboring devices through the Beacon Period Occupancy Information Element (BPOIE) transmitted together within every beacon.
In order to support more than 24 devices in different groups operating simultaneously, the MBOA MAC protocol allows devices to create and broadcast their beacons in new BPs different from existing ones. This means that in a superframe of a device, there can be multiple BPs used by other neighboring devices. Another reason for having multiple BPs is network merging between 2 or more Beacon Groups (BG), illustrated in FIG. 2. A BG is formed by 1 or more devices beaconing in the same BP.
The MBOA MAC protocol allows devices within the same BG to communicate. Since each device listens in the BP of the local cluster around each device, data reservation announcements in the BG can be heard via beacon frames. However, for a device to communicate with another device in another BG, the communicating device is required to beacon in the target device's BP as well.
When a neighboring BG is detected, first the local BG informs the devices in the local BG of the presence of the neighboring BG via the beacon of the local BG. In addition, the local BG attempts to inform the neighboring BG if the local BG determines that the local BG is not protected in the same way as the neighboring BG. To do so, the local BG transmits a beacon frame in the BP of the neighboring BG for a number of consecutive superframes. The BS the local device uses is chosen at random from the list of available vacant slots.
In mandating a device to beacon in a neighboring BP so that data communication is enabled across BGs, unnecessary beaconing is imposed on the beaconing device.
To protect the neighboring BG, a device sends out a reservation request to block devices in the local BG from using the BP of the neighboring BG. In the case of multiple neighboring BGs having one or more BPs overlapping, a device has to send this reservation multiple times.
When making a neighboring BG announcement, a device uses a BS of the neighboring BG's BP. The neighboring BG's BP may be running low in available BSs and this might cause new devices not being able to join the neighboring BG. In addition, if there are no more BSs available, that neighboring BG cannot be informed of the presence of the local BG.
In addition, if multiple BGs make announcement beaconing to the same neighboring BG, announcement beacon frames may colloid. This makes announcement beaconing unreliable.